高細粒料土壤動力三軸試驗試體孔隙水壓激發之探討

Pore Water Pressure Generation with High Fines Content Specimens in Dynamic Triaxial Tests

葉俊麟(Chun-Lin Yeh)

指導教授 ： 翁作新

國立臺灣大學/工學院/土木工程學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.00951

摘要

摘　要
一般動力三軸試驗於液化試驗中，如CKC動力三軸試驗儀常以硬管線連接孔隙水壓量測系統於試體頂座與底座，三軸試驗在不排水情況下，試體及量測系統均假設沒有體積變化，但實際上體積變化是存在於整個動態三軸試驗系統，如壓力變化對管路截面積、孔隙水壓感應子等之量測設備均會造成體積改變。因此當試體某一點孔隙水壓變化時，在其他位置的土壤或管路之另一端水壓計，因為上述試驗系統之體積變化，則必須要有水流產生，才能感受到此變化。這對於純淨砂透水性高的試體，水流流動可迅速傳達至孔隙水壓感應子來即時反應孔隙水壓；然而，在高細粒料含量或細粒料土壤之試體，因其孔隙比較小，透水性較低，而水流流動相較於純淨砂試體亦較慢，使得孔隙水壓感應子在試體兩端量得之孔隙水壓變化，在較快動態載重作用頻率下，不足以即時反應土壤內部之孔隙水壓情況。

針對上述問題，本研究結果指出在土壤動態試驗中，具細粒料成分之試孔隙水壓量測之主要影響原因如下；

(1)土壤滲透性(Permeability)，不同細粒料含量土壤試體，其試體滲透性質亦不同，細粒料含量較高試體，通常會有較低的滲透性，使前述孔隙水壓量測系統較不易即時反應土壤內部之孔隙水壓情況。

(2)反覆載重作用頻率(Frequency)，比較在同樣應力比情況下，當載重作用頻率較高時，單位時間載重施加較為迅速，使得前述水壓量測設備因系統體積變化，而無法即時反應試體內部水壓情況。相反的當載重作用頻率較低時，施加載重作用時間延長，其系統水壓量測比較能反應試體內部之狀況。

(3)反覆剪應力比(Cyclic Stress Ratio, CSR)，採用較大反覆剪應力比時，將會激發較大超額孔隙水壓力，使管線有較大體積變化，也較容易影響試驗系統孔隙水壓量測之結果。

關鍵字

砂 ； 細粒料含量 ； 液化 ； 三軸動力試驗 ； 孔隙水壓 ； 反覆剪應力比

並列摘要

Pore Water Pressure Generation with High Fines Content Specimens in Dynamic Triaxial Tests

Abstract

In the typical CKC cyclic triaxial tests, the researchers often use small and stiff tubes to connect the cap and bottom of the specimens to the pore water pressure sensors. They assume that there is no change in the volume of specimens and measure systems in undrained tests.

In fact, the volume change exists in the triaxial measurement systems when water pressure changes. Therefore, when the pore water pressure changes in certain location of the sample, the soil in other location or at another end of the water pressure measurement of the pipeline can experience the pressure change only when water flow occurs. Flowing can occur and reflect the pore water pressure change rapidly for sand of high permeability, but there is lower permeability in the sand of a high fines content. The pore water pressure measurement cannot reflect the pore water pressure changes within the specimen immediately.

This research pointed out the major factors of pore water pressure measurements for high fines content soil in dynamic triaxial tests as follow:

(1)Permeability: There are different permeabilities for soils of different fines contents. The higher fines content the lower permeability of the soil, so it cannot reflect true pore water pressure situation within specimen immediately in the pore water pressure measurements.

(2)Frequency of cyclic loading: There is a longer duration of loading during tests of lower frequency, and pore water pressure measurement can obtain better pore water pressure within the samples.

(3)Cyclic stress ratio, CSR: Higher pore water pressure changes usually occur in the triaxial tests with larger CSR, and result in more volume change in the pipeline section.

並列關鍵字

sand ； fine content ； liquefaction ； dynamic triaxial test ； pore water pressure ； cyclic stress ratio

參考文獻

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